You should give us some system specs. Like processor speed, RAM, and maybe even harddrives. My first guess is that your computer is doing something called swaping or virtural memory, and has to write stuff to your hard disk while using memory intensive programs. Check the HDD LED on your PC Case to see if that is the case during the slow downs. If so, simply don't run as many programs, or put more RAM into your PC. Defragmenting your Hard Drive might also help so it can do faster sequental writes during this process instead of random writes.

The idle process isn't really a program, it is simply showing that the CPU is inactive. It is calculated by adding up all of the processes in the process list and subtracting them from 100%. Its priority is idle, that is if something can be done instead of it it will be done. If you are trying to do something on your computer and it is 99% idle and everything is sluggish, I highly suggest you ensure your computer isn't running stuff it isn't supposed to. I don't know for sure, but some stuff is rumored to hide from the Task List, and thus their usage would fall under idle.

Basic Check (Gets desperate towards the end):
1) Check the Startup folder in your Start->Programs menu from the start bar. Find programs that don't fit in there. Double click it to open it in a folder, and show all hidden files.
2) Check the system services, in Control Panel->Administrative Tools->Services. Usually unless you know something is out of place in here, you might not know what you're looking for.
3) Update and run a full virus scan. Sadly this may be useless advice since in some cases a virus can disable your antivirus.
4) Run a program to find spyware. Adware or Spybot Search & Destory might work. I don't think that spyware is quite this malicious and obvious to slow down your PC, so these might not detect them.
5) Create a new user account and use it. Sometimes a user might have some weird luggage following it so a new user *might* fix that problem. You may have to reconfigure some software.
6) Boot into Safe Mode (Press F8 right after BIOS I think), and see if the problem exists there. Safe Mode only starts what is completely necessary, so if the problem still exists here then the problem is probably too deep to fix. Maybe run some tests (HDD benchmarks since I think it would be an important hardware suspect, such as http://www.simplisoftware.com/Public...request=HdTach) to see if your hardware is running as it should. If benchmarks show your computer to be fairly quick, then consider backing up important data to a CD-R, and after everything of value is backed up try a restore with the WinNT/2K install CD. If that doesn't work, you might have to dump everything and go for a full reinstall, and if the problem still exists it is something with the hardware...

Hopefully the issue is something simple. Don't go for the very last few ideas until you are completely sure you want to. And definately keep us up to date. It sounds like a weird/interesting case, and you should get more people's opinions you before you seriously consider a reinstall.


PS: Hardware specs would help. RAM, CPU, HDD, etc... And how long ago this developed, and what you two remember doing similar in that time frame...